Preparation of a zinc aluminategroup vi metal oxide catalyst



Patented June 1949 U ITED STATES PATENT OFFICE PREPARATION OF A ZINCALUMINATE- GROUP VI METAL OXIDE CATALYST Kenneth K. Kearby, Cranford, N.J., assignor to Standard Oil Development Company, a corporation ofDelaware No Drawing. Application December 31, 1947, Serial No. 795,139

Claims.

either hydroforming or aromatization reactions.

By hydroforming is ordinarily meant an operation conducted at elevatedtemperatures and pressures in the presence of a solid catalyst and addedhydrogen, wherein a hydrocarbon fraction is increased in aromaticity andwherein there is no net consumption of hydrogen. The term aromatizationrefers to an operation in which a, hydrocarbon fraction is treated atelevated temperatures, but at substantially atmospheric pressure, in thepresence of a solid catalyst, for the purpose of increasing thearomaticity of the hydrocarbon fraction.

Catalytic reforming operations are usually carried out at temperaturesof around 900-1000 F. in the presence of such catalysts as molybdenumoxide, chromium oxide, nickel sulfide, or tungsten sulfide, or any of anumber of oxides or. sulfides of metals of groups IV, V, VI, VII andVIII of the periodic system. These catalysts are usually supported on abase or spacing agent and the most commonly used base is alumina, eitherof the gel type or precipitated alumina. For example, a modifiedalumina, made by heat treating hydrated aluminum oxide, has been used asa support or extending agent for the active reforming catalystsmentioned above. Thus, a good catalyst for reforming or hydroforming isone containing about 10% molybdenum oxide supported on an alumina base.However, alumina in its various forms is not heat-stable, particularlyat regeneration temperatures which are of the order of 1000-1200" F. Attemperatures in the neighborhood of 1100 F. or higher, alumina isdefinitely impaired by prolonged heating, and

this impairment is reflected in the loss of activity of the catalystcomposition of which the alumina is the support or spacing-agent.Consequently, since the aromatization of a parafiln, such as, forexample, normal heptane to form toluene, is an operation which requireshigh temperatures, the ordinary alumina base does not withstand thetemperatures necessary for this particular conversion for a prolongedperiod of time.

A method has now been found for treating alumina to increase its heatresistance so that it may act more efliciently as a support for hightemperature catalytic processes, such as reforming and aromatization,and will have a high degree of activity under the most severetemperature conditions for an extended period of time.

.In this invention the catalyst base or support is prepared by combiningaluminum oxide with zinc oxide, preferably in molecular proportions,thereby forming zinc aluminate. This combination forms a true compoundof the spinal type and is not merely a mechanical mixture, forexamination of the lattice spacing in accordance with the well knownprocedure of X-ray diflraction proves that the combination is a truechemical compound.

It has now been found not only that zinc aluminate spinel is more heatstable than ordinary alumina but also that molybdenum oxide and chromiumoxide are much more active catalysts when supported on zinc aluminatespinel than when supported on alumina.

While the new catalysts of this invention are particularly suitable foruse in the aromatization of aliphatic hydrocarbons at high temperatures,

the improved catalysts are also superior to those formerly used inreforming or hydroforming operations.

The main object of the present invention is to provide aheat-stable'base or spacing agent for active reforming and aromatizingcatalysts and particularly for oxides of group VI of the periodic table.Another object of the invention is to provide a more activedehydrogenation catalyst especially for aromatizing or hydroformingnaphthas, particularly from the standpoint of .yields of aromatics inthe reformed product.

Another object of the invention is to provide means for synthesizing aheat stable base or spacing agent for active oxide catalysts. A morespecific object of the invention is to modify alumina chemically so asto render it more heatstable and capable of being used at hightemperatures as a supporting base for molybdenum oxide, chromium oxideand other group VI oxide catalysts.

Other and further objects of the invention will appear from thefollowing more detailed description and claims. Briefly, the newcatalyst composition comprises a major proportion of a zinc aluminatespinel to which has been added a minor proportion of a group VI oxide.More specifically the catalyst composition comprises from about to aboutzinc aluminate spinel and from about 5% to about 30% of a group VI oxideor of mixtures of these oxides. Compositions containing from 10% to 20%of molybdenum oxide or of chromium oxide or of mixtures of these oxidessupported on zinc aluminate spinel are particularly effective.

Briefly, the preferred method of preparing the new catalyst compositionsof the present invention is about as follows: An acidic solution of azinc salt such as zinc nitrate or zinc sulfate is allowed to react witha basic solution of an alkali metal aluminate such as sodium aluminate.Zinc aluminate precipitate is separated from the resulting slurry and iswashed with water, dried and then calcined at about 1000-1200 F. A groupVI metal oxide is incorporated into the zinc aluminate precipitateeither before or after the drying and calcining treatment. A convenientmethod for doing this is to impregnate the precipitate with a solutionof a salt of the desired metal and then convert the salt to thehydroxide or oxide by adding a base such as ammonium hydroxide.

Methods for preparing the new catalyst compositions are set forth below:

EXAMPLE 1 Solution A.9'74 g. of C. P. zinc nitrate,

Zn(NOs)2.6H20, was dissolved in a solution of 1'79 cc. concentratednitric acid in 2 liters of distilled water and made up to a volume of3290 cc.

Solution B.80 g. pure NaOH was dissolved in 4 liters of distilled water.800 g. of sodium aluminate was stirred in rapidly. After stirring fortwo minutes, 500 cc. of a diatomaceous earth filter aid was added.Stirring was continued for one-half minute and the suspension wasfiltered on a Biichner funnel. 3290 cc. of the filtrate was used forsolution B. The resulting solution had a concentration of 101 g. A120:and 87 g. NazO per liter. On this basis, the acidity of the zinc nitrate(solution A) was adjusted to exactly neutralize the alkali of thealumina solution.

Solutions A and B were added at equal rates over a period of 30 minutesto liters of distilled water while stirring. Stirring was continued forminutes after all of A and B had been added and the precipitatefiltered. The precipitate was washed with 6 liters H2O, restirred in 12liters of water, filtered and washed with 6 liters H2O. The precipitatewas dried and calcined 3 hours at 1000 F.

The zinc aluminate was mixed for3 hours in the ball mill with a solutionof 81.8 g. of C. P. ammonium molybdate dissolved in a mixture of 44 cc.concentrated ammonium hydroxide in 440 cc. 11 0. (Additional water wasadded, sufficient to form a thick paste before mixing.) The mixture wasdried v pilled and calcined for 3 hours at 1000 F. s I

EXAMPLE 2 Another catalyst was prepared as above except that the washedzinc aluminate precipitate was not dried and calcined before mixing withthe ammonium molybdate solution.

EXAMPLE 3 mixed with '4 liters of distilled water. The filtrate was notclear and was used to resuspend and mix the zinc hydroxide and aluminumhydroxide precipitates. The mixture was filtered 5 and washed on thefilter with 3 liters of water. It was mixed for 3 hours in the ballmill, dried and calcined for 3 hours at 1000 F.

The product was impregnated with ammonium molybdate (40.9 g.) andfinished as in Example 1.

The catalyst supports prepared according to the foregoing procedures aretrue compounds having the formula ZnO.A12O3. This has been establishedby comparison of the X-ray diffraction pattern of the catalyst base withpublished patterns for zinc aluminate. The comparison is tabulatedbelow:

Standard Literature 5 Values Measured on present Catalyst Base Gamma ZnOesaasssa 1 Weak lines.

I Major lines ior alumina.

See Ind. 6: Eng. Chem. Anal.-Ed., 10, 510, 511 (1938); and Gamma A1703from card die of Amer. Soc. for Testing Materials, W. P. Davey,Chairman, Penn. State College.

It will be noted that the catalyst support prepared as set forth in theleft-hand column com- 40 pares very favorably with the literature datagiven for the compound ZI1A12O4. In columns 3 and 4 are set forth,respectively, the data given in theliterature for zinc oxide andaluminum oxide, and it is clear from these data that-the new catalystsupport is not a mere mechanical mixture of these two substances, sincesuch a mixture would give superposed patterns of ZnO and A1203. Forexample, in the aluminum oxide column there are no lines whatevercorresponding to the 2.86 or 2.45 Angstrom spacings of the sample, .andunder the zinc oxide column given in the foregoing table there areblanks corresponding to the 2.02 and 1.652 lines of the sample, and inthis same connection at the corresponding points in columns 3 and 4under zinc oxide and aluminum oxide, the lines differ beyondexperimental limits of error (.02 Angstrom unit) from those determinedby test of the new catalyst base. Hence the compound comprising the baseof this new catalyst cannot be a mere mechanical mixture of zinc oxideand aluminum oxide, but is an entirely different crystalline compound.

EXAMPLE 4:

To test the new catalysts three runs were made to aromatize normalheptane. These runs were all conducted at 1000 F., at a feed rate of 1.2volumes of normal heptane per volume of catalyst per hour, at aboutatmospheric pressure. In run A parts of the improved base, that is, zincaluminate spinel was used, and 10 parts by weight of M003; in run 3"chromium oxide on alumina was used, the amount of CrzOs being 11% byweight of the mixture; and in run C a catalyst consisting of about 10%by weight of molybdenum oxide on alumina was employed. Set forth beloware the results of these runs:

min A o 117 :10; 10% M0 lumina 1 on on Liauid Recovery, Vol. Per

ent Aromaticity, Vol. Per Cent...

68 Total Aromatic Yield, Vol.

Per Cent EXAMPLE 5 When testing the suitability of the catalyst of thepresent invention in aromatization of a naphtha feed, it was found thatthe catalyst was superior to the known reforming catalysts describedabove. Thus. using a naphthenic feed stock, 1

'lhe iced had the following inspection: gravity A. P. I. 55.7; per cent8. 0.0058; Br. No.=0; Reid vapor pressure=1.2 lbs./sq. in.; vol. r centaromatics=1l.2; vol. per cent methyl cyclohexane and ethylcyclopentane=26.2; vol. per cent naphthenee=47.3; vol. per centparafilns=4l.5; boiling range=200270 F.

five runs were made using the improved catalysts in three andalumina-supported catalysts in two, operating in all five runs at a feedrate of 1.2 volumes of liquid feed per volume of catalyst per 1101113315a temperature 01 1000 F. and atmospheric pressure (one hour period). Thefollowrepresents a cross aromatic yield of 66 volume per cent on teed.

Influence of feed rate and temperature on the dramatization of uaphthaover zinc aluminate- Feed contains 11% aromatim; naphtha ssuw'asdescribed in Example 5.

I Volume oi liquid iced per volume of catalyst per hour. fl Includesaromatics present in Iced.

Page 7 other runs were conducted to test the value or the new catalystin hydroforming. In these runs an East Texas naphthenic naphtha(described in Example 5) was treated under conditions set forth below,in one case using the catalyst of the present invention and in the otherrun .using a conventional hydroforming catalyst consisting of alumine.supporting molybdenum oxide, the latter being one of the besthydroforming catalysts heretofore developed. It will be observed in thedata presented below that the use of the zinc alumlnate molybdenum oxidecatalyst gave superior results, for it will be noted that thearomati'city. the gross yield, and the conversions were much higher inthe case oi the zinc spinel supported ing results were obtained: 40catalyst than in the case of the conventional hy- Pm by Wt toe znAno.009' 211.4110. 117 0110, 107.1400, 85% 21mm 10 M00; 0 (m0; on Xlumina onXlumina f f Li ma Becove Vol. r cent 11 so. a a 81 as 15. 5 *:i."'.itiiti-s"" s s: s s e cen $8122 wgf l er cen 6.6 4.5 4.6 4.6 6.3

EXAMPLE 6 In other runs it was found that by decreasing the naphtha from1.2 volumes to 0.45 volume of naphtha. per volume of catalyst per hour,but otherwise operating under the same conditions, namely, a temperatureof 1000 F. and atmospheric pressure, the aromaticity of the producttemperature to 950 F. even better results were obtained at lower feedrates, namely. at 0.25 volume of liquid naphtha per volume of catalystper hour. At a feed rate of 0.25 volume of naphtha per volume ofcatalyst per hour a 69% liquid yield having an aromaticity or 95% wasobtained. This Ten i perature, F 005 Liq d Recovery, Vol. percent 83. 4Gas, Wt. percent 11.5 g 'ati i'tg v 1 "i' '5 m 0 can Oleilnicity, in: WV

'was increased from '71 to By lowering the 70 droforming catalyst. Thesedata, together with operating conditions, are set forth below:

[ d-hour pertods; 1.27 v./v./hr. feed rate: moo C. RIB. 1 0/ Hz; 200lbs. per sq. in. metal znmioa, $1.83? 10% M00.

Catalyst 1 Cubic feet per barrel. I Fraction of non-aromatic portion offeed which reacts.

EXAMPLE 8 The eil'ect of pressure in hydroforming is shown by thefollowing data- In each case the feed was a 200-270 F. naphtha or thetype used in Example 5 and the catalyst was 10% molybdenum oxidesupported on 90 zinc aluminate. Duration of each run was one hour. Itwill be seen thatin general coke formation is reduced as the pressure isincreased and aromatic yields are improved as the pressure is reduced.

Efiect of pressure in hydroforming using zinc aluminum-molybdenum oxidecatalyst The following runs show that when aromatizing naphtha atatmospheric pressure dilution of the feed with hydrogen has a markedeflect in reducing coke formation and also results in a slightly higheryield of aromatics at a given liquid recovery. Thus, at 950 F., 0.25v./v./hr., dilution of the vaporized feed with two volumes of hydrogen(2 volumes hydrogen S. T. P. per calculated volume S. T. P. of feed)decreases coke formation from 7.2% to 3.7%, and results in an increasein liquid recovery from 69% to 72%, at about 95% aromaticity. A furtherreduction in coke formation to 2.5 wt. percent On feed is obtained byincreasing the hydrogen dilution ratio to 4/1. A similar trend isobserved at 1000 F., 1.2 v./v./hr.

These data are summarized in the following table:

Influence of hydrogen dilution on the aromatization of naphtha over(90%) zinc aluminate- (10%) molybdenum oxide catalyst 1 Same naphtha asdescribed in Example 5.

Since the gaseous reaction products are largely hydrogen, it wouldappear that recycle of a portion of the make gas would be an effectiveway to reduce carbon formation.

Exmu: 10

Further runs were made to test the suitability of the new catalystcompositions in reforming naphtha at various temperatures and feed ratesnd these data are summarized below:

5 sirable.

35 of water.

fate and a soluble aluminum compound, S04 radical is occluded in theprecipitate and cannot be washed therefrom with water. The presence ofsulfate in the zinc aluminate spinel is unde- For example, it has beenfound that when the zinc aluminate spinel base contained 6.1 per cent$04 by weight'and was employed to aromatize normal heptane underconventional testing conditions, 44 per cent aromatics, based 10 onfeed, was formed. On the other hand, when the same base, tested underidentical conditions in aromatizing normal heptane, contained 12 percent by weight S04, the yield of aromatics was only 31 per cent based onfeed. While it is pos- 15 sible to reduce this sulfate content bywashing with alkaline solutions or by treating the catalyst at elevatedtemperatures with hydrogen and steam, these procedures are lesspreferable than using direct methods of preparing catalysts having a lowcontent of sulfate.

The methods outlined below for the preparation of zinc aluminate fromzinc sulfate can also be applied to the preparation of this materialfrom zinc'chloride, since here also the problem of reducing theocclusion of anions without favoring the occlusion of sodium isencountered. Two methods of preparing the zinc aluminate spinel fromzinc sulfate are as follows:

30 EXAMPLE 11 1416 g. of C. P. zinc sulfate and 105 cc. of concentratedsulfuric acid were dissolved in water to make 5049 cc. of solution A.1200 g. of sodium aluminate was stirred for 10 minutes in 6000 cc. Oneliter of filter aid was added and the solution was filtered. 5049 cc. offiltrate was taken as solution B. Five liters of water was stirredvigorously in a 5-gallon crock while solutions A and B were addedsimultaneously and 40 at the same rate over a 30-minute period. More'water was added during the precipitation to facilitate stirring. Afterthe final slurry had been stirred 10 minutes the pH of the supernatantliquid was found to be 10.

The slurry was filtered and the cake was washed with 18 liters ofdistilled water. It was restirred with distilled water and divided intothirds. Two thirds was set aside for other tests. The other third wasslurried in 6 liters of distilled water; filtered and washed with 6liters of distilled water. The cake was reslurried in 6 liters ofdistilled water, filtered and washed with 8 liters of distilled water.The cake was made into a thick Catalytic dramatization ofnaphtha over90% zinc aluminate-10% molybdenum oxide catalyst [Atmospheric pressure]900 950 50 950 950 950 950 1, 000 l, 000 l, 000 1, 000 1, 000 l, 0000.45 1.2 045 0.25 0.26 0-25 0.25 .48 1.2 1.2 1.2 1.2 1.2 3 1 3 3 6 3 3 31 1 1 1 l H; Dilution Ratio 0 2- l 0 0 2.0 0 0 4. 2 0 0 0 0 1.8 4 2Liquid Recovery,Vol.Per Cent. 84. 4 81. 5 84.3 77. 3 82. 0 73. 2 88.872. 4 67. 7 76 0 77. 5 I 80. 3 82. 3 76. 3 Aromaticity, Vol. Per Cent 6161 74 73 93 95 95 85 69 61 68 62 05 Aromatic Yield, Vol. Per Cent. 51 4945 57 68 66 69 57 52 47 55 51 49 Coke, Wt. Per Cent on Feed" 4.3 2 0 4.65. 8 3. 3 5. 9 7.2 2. 5 l0. 9 5. 3 7. 2 6. 7 2. 4 2. 2 Gas, Wt. Per Centon Food... 6.8 9.8 6. 6 l0 6 7.0 11. 4 14.0 15.0 13. 3 12. 5 8. 9 7.8 9.6 13.2 Catalyst Age, Cycles 1 9 11 6 7 10 3 1- 3 2 o 4 3 5 4 Run No 176179 176 176 179 184 188 188 184 184 164 176 164 18s I N aphtha same asused in Example a I A cycle is a period on-stream and a period ofregeneration with a mixture of air and inert gas (usually 2 hours).

In the foregoing examples the zinc aluminate base was prepared usingzinc nitrate as starting material. It is also possible to prepare zincaluminate from zinc sulfate as starting material but in this casecertain precautions must be observed. One of the problems is that whenthe zinc aluminate is precipitated from a solution of zinc sulpaste withdistilled Water and was mixed with a solution of 40.9 g. ammoniummolybdatein a blend of. 25 cc. concentrated ammonium hydroxide plus 250cc. of distilled water; This gave a composition of 90 parts by weight ofZI1A12O4 and 10 parts by weight of M003. The mixture was ball milled 3hours, dried with stirring, calcined This time the 400 F. The wetmaterial was stirred occasionally to insure uniformity. The driedproduct Catalytic dramatization [1000 F. 1.2 v./v./hr.; 1 hr. periods: 1atm, pressure] Percent Percent Vol. Percent Conver- Selectivity Net Aro-Gas Coke sion to Aromatics matics -H tane Feed 80 55 44 16.5 5.9 all-370 F. East Texas Naphtha Feed 85 53 45 10. 8 8:. 7

Exsmrnr. 12

In this example the ZnOAhOa was prepared on the basis of giving 25pounds of finished catalyst. The amount of sodium aluminate solutionrequired when made by the standard procedure described below wascalculated to be 57.3 liters. From the alumina and sodium hydroxidecontent of this'solution the required amounts of zinc sulfate andsulfuric acid were calculated.

Thirty-five and thirty one-hundredths pounds of technical zinc sulfateand 986 cc. of concenwas calcined 3 hours in an electric muflie at 1200F. and then pilled.

NOTE..The pHs given above were determined with a commercially availabletesting paper. Checks with a glass electrode pH meter have indicatedthat the paper values of 12 to 13 correspond to glass electrode valuesof approximately 10.5 to 12 and a paper value of 7.5 gives an electrodevalue of 8.5.

When tested as a catalyst, the following results were obtained: I

' Catalytic aromatz'zation [1000 F. 1.2 v./v./hr. 1 hr. periods 1 atm.pressured Percent Percent Se- Vol. Percent Converlcctlvity to Gas Cokesion Aromatics Aromatics n-Heptane Feed 77 65 42 14. 0 ZOO-270 F. EastTexas Naphtha Feed 78 64 42 9.3

trated sulfuric acid were dissolved in water to give 57.3 liters ofsolution A. Thirteen kilograms of sodium aluminate was stirred for 15minutes in 65 liters of water. About 6 liters of filter aid was stirredin and the mixture was filtered with a filter crock. Fifty-seven andthree tenths liters of the filtrate was taken as solution B.

Twelve liters of water was poured into a 50- gallon barrel and stirredvigorously while solutions A and B were added simultaneously and at thesame rate from calibrated bottles during a period of one hour.

The pH of the liquid portion of the slurry was found to be 12. Portionsof sulfuric acid diluted to 1 were added with stirring until the pH wasreduced to 7.5. (Three hundred and fifty cc. of concentrated sulfuricacid diluted with 7 liters of water was added in all.)

The slurry was then pumped into a filter press containing ten plates, 1"by 18"by-18". At a pressure of 65 pounds persquareinchonlyaboutseveneighths of the slurry could be-pumped into the press. Thematerial in the press was washed with 60 gallons of water per hour for 3hours. It was then air blown for minutes and dumped. The cake wasresuspended in water in a 50 gallon barrel and left overnight. The nextmorning the slurry was againpumped into the ten-plate press. press wasnot filled, indicating shrinkage of. the precipitate. The press waswashed with water at the rate of 150 gallons'per hour for 3 hours. Itwas then air blown for half an hour and dumped.

The cake was worked into a very thick paste by means of largepropeller-type stirrers. The water added in this step was kept to aminimum. A solution of 1220 g. of C. P. ammonium molybdate dissolved in9 liters of water was then stirred into the paste to form a thick slurrywhich was allowed to stand overnight. The slurry was then dried in anoven with air circulation at 240 to ing' the precipitation within therange of from 9 to 12, the quantity of sulfate radical occluded in theprecipitate is restricted to an amount not exceeding 5 percent byweight. At the same time, by adjusting the final pH of the filtrate to avalue between 7 and 8, the sodium was desorbed in the final precipitateso that it did not exceed about one-tenth of 1 per cent and thus wasassured the production of catalysts of reproducible activity.

In the two preceding examples are disclosed methods of .forming the zincaluminate spinel base in which two solutions were mixed, namely zincsulfate containing sulfuric acid and sodium aluminate containing sodiumhydroxide. Instead of so proceeding, a solution containing zinc sulfateand aluminum sulfate may be mixed with an alkali such as sodium orammonium hydroxide.

It will be understood, however, that in these modifications the sameprecautions must be observed as regards the pH of the supernatant liquidin the precipitating medium, including the final adjustment thereof.

Instead of using a commercial sodium aluminate, one may use an aluminumoxide, such as AI2O3.3H2O dissolved in an alkaline solution.

In any of the methods of preparing zinc aluminate, whether from zincsulfate, nitrate or other salt, it is to be understood that sodiumcarbonate may be used in place of sodium hydroxide as precipitatingagent. Also by conducting the precipitation at 60-100 0. rather than atroom temperature catalyst bases of lower density and increased pore sizemay be prepared.

As previously indicated, the zinc aluminate composition prepared fromthe zinc sulfate is In the preceding examples care was taken to by thefollowing data:

Catalytic aromatization [1000 F.; 1.2 v. v./hr. Catalyst composition:10%

o 90% ZnAhOa] 6 Hrs. in Stream 3 Hrs. in Mums Calcination at 12000 F ofat Zinc Belt Used in Prep.

of st. Base Nitrate Sulfate Nitrate Sulfate Vol. Per Cent Net Aromatics:

n-Heptane Feed- 45 42 36 40 East Texas Virgin V Naphtha Feed.. 42 42 3239 This is important because in preparing the catalyst the material iscalcined ordinarily in a kiln and the more heat stable catalyst does notre quire the critical control that the less heat stable catalystrequires; and, furthermore, in the regeneration of the catalyst afteruse in, say, hy-

droforming or aromatizing operations, the more heat stable catalyst isless liable to injury during regeneration, an operation usuallyperformed by burning off the contaminants formed on the catalyst duringuse in the on-stream operation.

Another advantage of the catalyst prepared from the zinc sulfate is thatof increased activity as set forth below in the following data:

Catalytic aromatization [1000 F.; 1.2 v.lv.lhr.; 1 hr. period. Catalyst:10% M003 on 90% ZnAhOi (ti-om 211800 .1

These results are higher than ever obtained from the same type ofcatalysts tested under similar conditions but in which the catalyst basewas zinc aluminate that had been prepared from him nitrate. In the runsset forth in the two preceding tables, the pressure in the reaction zonewas approximately 1 atmosphere and no added hydrogen was present in thereaction zone.

Instead of coprecipitating the zinc and the alumina, one may separatelyprecipitate zinc hydroxide and aluminum hydroxide from any suitablesource and thereafter mix the precipitates in suitable proportions toform the zinc aluminate. The mixture is then dried and finally calcinedat above 800 F. and preferably at above 1000 F. Addition of the group VIoxide may be successfully accomplished either before or after the dryingprocess. For example, molybednum oxide may be coprecipitated from asolution of 12 an alkaline molybdate either at the same time the zincaluminate is precipitated or at some later point in the preparation ofthe zinc aluminate.

Alternative methods of preparing zinc aluminate include: reaction ofsodium zincate or of ammonium zincate with aluminum sulfate or nitrate;admixture of sodium aluminate and sodium or ammonium zincate andcoprecipitation with sulfuric or nitric acid; and precipitation ofadmixed sodium aluminate and sodium or ammonium zincate with zinc andaluminum sulfates or nitrates. Still another method is to convert zincand aluminum chloride into zinc and aluminum oxide gels by reaction withethylene oxide. Also; zinc and aluminum or their alloys may be convertedto sols by action of dilute formic or acetic acid in the presence ofmercury salts.

When using any of the methods given herein for the preparation of zincaluminat it may be found advantageous to modify the gelatinous nature ofthe product by conducting the preparation in the presence of 1 to 10%(based on the dry catalyst) of an acetate, tartrate or citrate, e. g.,ammonium acetate, or of 0.5% to 5% of a silicic acid sol or of glycerol,starch, vegetable gums and the like. 4

To review briefly, it has been found that when alumina is modified byreacting it with a zinc compound to form a complex compound containingthe zinc, in other words, zinc aluminate, the resulting product is moreheat stable than aluminum oxide. Furthermore, the activity of molybdenumoxide and chromium oxide catalysts is greater when using zinc aluminaterather than alumina as the base or support. The improved base makes itpossible to obtain good yields of aromatics by aromatization ofparaflins and it also improves the hydroforming process, since itresults in the formation of increased quantities of aromatics in theproduct which is a highly desirable result since these aromaticsincrease the octane rating of the said product. A number of other heavymetal divalent oxides have been tried as substitutes for zinc oxidewithout securing any definite improvement in the alumina base.

This is illustrated in the table presented below. These data wereobtained in aromatization tests conducted by the method employed inExample 4. All these tests were run at 1000 F. using a feed rate of 1.2volumes of normal heptane per volume of catalyst per hour at aboutatmospheric pressure. The catalyst in each case consisted of 10%molybdenum oxide supported on the catalyst base indicated.

Aromatization of n-heptane [1000 F.; 1.2 v./v./hr. 1 hr. periods.]

spinel was much better than alumina as a catalyst support all of theother metal aluminates were no better than or inferior to alumina.

Although from 5 to 30% of a group VI oxide or of mixtures of theseoxides may be employed in these catalyst compositions, from about toabout 20% of these oxides is particularly desir- 'able. The effect ofvarying the molybdenum oxide content of the zinc aluminate-molybdenumoxide catalyst composition is shown in the following table of dataobtained under aromatization conditions, that is, at atmosphericpressure and with no added hydrogen.

Eflect of M003 content on catalyst activity [1000" F., 1.2 v./v./hr.feed rate, 1 hr. perloda] It is to be understood that these newcatalysts may be used in a number of reactions other than thosedisclosed specifically above. For instance,

they may be used in the dehydrogenation of' paraifins to olefins or ofolefins to diolefins, desulfurization of sour petroleum oils,oxidations, destructive hydrogenation of petroleum oil, coal tar oil,coal, etc.

Although it is preferable that the zinc aluminate catalyst base beprepared by combining aluminum oxide and zinc oxide in molecularproportions, slight excesses of either component are not harmful. Thusan excess of either reactant may be used in making the zinc spinel orone may admix a slight excess of either ZnO or Alzm with the zincspinel. Furthermore, it has been found that addition of smallpercentages of promoters is sometimes beneficial, for example, 0.1 to0.5%

of Ni or Pt. Addition of 0.5 to 5% of calcium oxide to the catalystcompositions may be made when it is desired to improve the resistance ofmolybdenum oxide to oxidation and reduction.

These catalysts may be formed into pills,,pellets, or other shapedbodies either before or after the calcination and with or without theuse of pilling aids, such as graphite, starch, solid hydrogenatedvegetable fat, etc. The pellets and other shaped bodies may also beformed by extrusion methods. One good method of forming the catalystsinto desired shapes is to dry the precipitate in a high humidityatmosphere. For example, a one-inch filter cake can in this way be driedinto granules, 90 per cent of which will have a particle size of 2 to 8mesh. This method of forming the catalyst into desired shapes isimportant for the reason that it is much less expensive than when thecatalyst is formed into pills using pilling machinery.

Of course, in the case where the catalyst is to be used in what is knownas a fluid catalyst system, it may be ground either before or aftercalcinatlon to a size range smaller than 500 microns, preferably withinthe range of 20 to 200 microns. The dried or calcined material from thisgrinding operation which is too fine to use may be mixed with wetcatalyst in order to agglomerate it into a usable coarse size range.

It 'will be understood that these catalysts after use in aromatizationoperations or during hydroforming, and having become contaminated withcarbonaceous deposits, may be regenerated by burning off thecarbonaceous deposits by treatment with an oxygen-containing gas. Thisregeneration may be accomplished in a normal manner, conventional in theart except that these new catalysts are more heat stable than theordinary hydroforming catalysts such as those oxides which are supportedon an alumina base.

Numerous modifications of the invention falling within the scope thereofmay be made by those familiar with this art.

What is claimed is:

1. A process for preparing a catalyst adapted for the reforming ofhydrocarbons to increase their aromaticity which comprises interactingan .acidic solution of a zinc salt with a basic solution of an alkalimetal aluminate to form a slurry containing zinc aluminate precipitate,separating the precipitate from the resulting slurry, washing theprecipitate so separated, drying the washed precipitate, thereaftercalcining the dried precipitate for several hours at a temperature ofabout 1000-1200 F., and incorporating a group VI metal oxide into saidprecipitate to form a catalyst comprising a zinc aluminate spinel as amajor constituent and a group VI metal oxide as a minor constituent.

2. Process defined by claim 1 wherein the alkali metal aluminate issodium aluminate.

3. Process defined by claim 1 wherein the group VI metal oxide comprisesmolybdenum oxide.

' 4. Process defined by claim 1 wherein the group VI metal oxide isincorporated into said zinc aluminate precipitate before said calciningtreatment.

5. Process defined by claim 1 wherein the group VI metal oxide isincorporated into said precipitate following said calcining treatment.

6. Process defined by claim 1 wherein the zinc salt is zinc nitrate.

7. Process defined by claim 1 wherein the zinc salt is zinc sulfate.

8. A process for preparing a catalyst adapted for the reforming ofhydrocarbons to increase their aromaticity which comprises interactingan acidic solution of a zinc salt with a basic solution of sodiumaluminate to form a slurry containing zinc aluminate precipitate,separating the precipitate from the resulting slurry, washing theprecipitate so separated, impregnating the precipitate with ammoniummolybdate and ammonium hydroxide, drying the impregnated precipitate andcalcining the dried impregnated precipitate for severalhours at about1000-l200 F.

No references cited.

